Sulfonated naphthylamines containing the fiber reactive beta-hydroxyethylsulfone group or its reactive equivalent are important starting materials in the preparation of fiber reactive, water soluble azo dyestuffs. The sulfonation of such substituted naphthylamines is well known in the art. The sulfonation is carried by reacting the substituted naphthylamine with fuming sulfuric acid (oleum) in sulfuric acid usually at elevated temperature.
It is well known in the literature that the sulfonation of aminonaphthalenes and aminonaphthalene monosulfonic acids results in a mixture of isomeric products; see e.g. Mechanistic Aspects of Aromatic Sulfonation and Desulfonation; Cerfontain, H.; Chapter 7; John Wiley & Sons, New York, N.Y. (1968). Isomeric sulfonation products are also produced when a naphthylamine substituted with the beta-hydroxyethylsulfone group are sulfonated.
These isomeric mixtures of the sulfonation reaction are separated in commercial manufacturing processes by the selective crystallization of one isomer over the other after drowning the reaction solution in ice and water usually containing an inorganic salt such as sodium chloride. For example, the sulfonation of 2-aminonaphthalene-6-hydroxyethylsulfone in sulfuric with oleum at temperature of 70.degree.-80.degree. C. gives rise to two isomeric products; the 1-sulfo and 8-sulfo isomers in a ratio of 95:5 parts, respectively. Upon drowning into ice and water containing sodium chloride, the 1-sulfo isomer is recovered as a precipitate by filtration. A certain portion of the 1-sulfo isomer and essentially all of the 8-sulfo isomer are lost in the filtrate because it is extremely difficult to recover at this point due to its high water solubility.
It is the object of this invention to provide a process of the direct preparation of sulfonated 2-aminonaphthalenes containing fiber reactive, sulfone substituent as a single sulfonation product and new dyestuffs prepared from such substituted 2-aminonaphthalenes.
Although the prior art discloses a general procedure for the preparation of sulfonated aminonaphthalene hydroxyethyl sulfones; see e.g., U.S. Pat. No. 4,046,754, col. 2, lines 59-68, col. 3, lines 1-15; there is no appreciation or recognition in the prior art of the regiospecificity of the process of this invention nor of the properties of dyestuff prepared using the 2-amino-6-(.beta.-hydroxyethylsulfonyl)-naphthalene-8-sulfonic acid. This compound is disclosed at column 3, line 9 of the '754 patent.